The present invention relates generally to fastener-driving tools used to drive fasteners into workpieces, and specifically to pneumatically powered fastener-driving tools, also referred to as pneumatic tools. More particularly, the present invention relates to improvements in a device or assembly which adjusts the depth of drive of the tool. Other types of fastener driving tools such as combustion, powder activated and/or electrically powered tools are well known in the art, and are also contemplated for use with the present depth of drive adjustment assembly. The use of “fastener driving tools” in this application is considered to encompass all such tools, suitable examples of which are sold under the PASLODE brand manufactured by Illinois Tool Works, Vernon Hills, Ill.
Power fastener-driving tools of the type used to drive nails, staples and other types of fasteners typically include a housing, a power source, a supply of fasteners, a trigger for operating the power mechanism and a workpiece contacting element. The latter component is typically reciprocally slidable relative to the housing and connected to the trigger mechanism in some way, so that the fastener will not be driven unless the tool is pressed against a workpiece. Examples of such a prior fastener-driving tool are disclosed in U.S. Pat. Nos. 4,629,106 and 6,543,664, which are incorporated by reference. Examples of such a prior fastener-driving tool is disclosed in U.S. Pat. Nos. 4,629,106 and 6,543,664, which are incorporated by reference.
One operational characteristic required in fastener driving applications, particularly trim applications, is the ability to predictably control fastener driving depth. For the sake of appearance, some trim applications require fasteners to be countersunk below the surface of the workpiece, others require the fasteners to be sunk flush with the surface of the workpiece, and some may require the fastener to stand off above the surface of the workpiece. Depth adjustment has been achieved in pneumatically powered and combustion powered tools through a tool controlling mechanism, referred to as a drive probe, that is movable in relation to the nosepiece of the tool. Its range of movement defines a range for fastener depth-of-drive. Similar depth of drive adjustment mechanisms are known for use in combustion type framing tools.
A conventional arrangement for depth adjustment involves the use of respective overlapping plates or tongues of a workpiece contact element and a wire form or valve linkage. At least one of the plates is slotted for sliding relative length adjustment. Threaded fasteners such as cap screws are employed to releasably secure the relative position of the plates together. The depth of fastener drive is adjusted by changing the length of the workpiece contact element relative to the wire form. Once the desired depth is achieved, the fasteners are tightened.
It has been found that users of such tools are inconvenienced by the requirement for an Allen wrench, nut driver, screwdriver or comparable tool for loosening the fasteners, then retightening them after length adjustment has been completed. In operation, it has been found that the extreme shock forces generated during fastener driving cause the desired and selected length adjustment to loosen and vary. Thus, the fasteners must be monitored for tightness during tool use.
To address the problem of maintaining adjustment, grooves or checkering have been added to the opposing faces of the overlapping plates to increase adhesion when the fasteners are tightened. However, to maintain the strength of the components in the stressful fastener driving environment, the grooves have not been made sufficiently deep to provide the desired amount of adhesion. Deeper grooves could be achieved without weakening the components by making the plates thicker, but that would add weight to the linkage, which is undesirable.
In other conventional tools, a fluted, threaded barrel is threadably engaged with a threaded end of a wire form workpiece contact element. Rotation of the fluted barrel adjusts the depth of drive. A biased, locking mechanism engages the flute to maintain position. In operation, impact forces have been known to cause unwanted movement of the barrel, changing the depth adjustment.
Other attempts have been made to provide tool-less depth of drive adjustment, but they have also employed the above-described opposing face grooves for additional adhesion, which is still prone to the adhesion problems discussed above.
Another design factor of such depth adjustment or depth of drive (used interchangeably) mechanisms is that the workpiece contact elements are often replaced over the life of the tool. As such, the depth adjustment mechanism preferably accommodates such replacement while retaining compatibility with the wire form, which is not necessarily replaced.
Accordingly, there is a need for a fastener driving tool depth of drive adjustment device or assembly where the adjustment is secured without the use of tools and is maintained during extended periods of fastener driving. There is also a need for a fastener depth adjustment device or assembly which provides for more positive retention of the relative position of the workpiece contact element without reducing component strength.